Fluorescence based methods for the detection of chemical and biological species area have attracted considerable attention because of their high sensitivity and ease of use and because instrumentation for these methods can be incorporated into small, compact devices that have low power requirements. These techniques frequently employ a fluorescent dye that interacts with a target analyte or family of analytes to produce a change in the fluorescence properties of the dye. These dye-analyte interactions may be signaled by changes in photoinduced properties such as absorption, emission intensity, or wavelength, and luminescence lifetime. Quenching of photoluminescence intensity is of particular interest as sensitivity is inherently enhanced due to a distinct contrast between signaling events (i.e., luminescent and nonluminescent states). See Martinez-Manez, R.; Sancenon, F., Chem. Rev. 203, 103, 4419. Researchers have utilized photoinduced electron transfer (PET), energy transfer, and other mechanisms to produce “on/off” sensors based on aromatic and polycyclic aromatic hydrocarbons, aromatic heterocycles, and transition metal complexes. See McQuade et al., Chem. Rev. 2000, 100, 2537 and Granda-Valdes et al., Quim. Anal. 2000, 19, 38.
A number of fluorescent sensor compounds have been developed for detecting saccharides. For example, U.S. Pat. No. 6,916,660 describes fluorescent anthracene molecules bearing boronic acids that selectively bind and detect various monosaccharides and polysaccharides. In addition, a number of metal-detecting fluorescent sensor compounds have been developed. For example, U.S. patent application Ser. No. 11/039,396 describes naphthofluorescein-based ligands that bind metal ions such as Hg2+ and Na+ with a concomitant change in fluorescence. The sensing of chemical warfare agents using chemosensors has also gained increasing attention. See McBride et al., Anal. Chem. 2003, 75, 1924. For example, Swager et al. reported functional group specific chemosensors that incorporated a transduction/cyclization process specific to highly reactive organophosphates and related compounds. See Zhang, S.-W.; Swager, T. M. J. Am. Chem. Soc. 2003, 125, 3420. However, there remains a need for chemical sensors that may be functionalized to respond to generic or specific target molecules.
Aromatic diimides have been employed extensively as fluorescent sensor dyes. Hoeben, et al., J. Chem. Rev. 2005, 105, 1491. An important requirement for the use of diimide linking groups in these systems is that the aromatic nucleus must be polarizable to allow facile charge transfer between donor and acceptor groups. With a very few exceptions, these efforts have been reported for naphthalene and perylene diimides due, for the most part that these systems can be readily prepared from commercially available naphthalene and perylene dianhydride. Accounts regarding anthracence-based imides, however, are limited due to synthetic challenges and limited solubility of anthracene-based imides. A versatile approach to preparing anthracene diimides would be highly desirable, enabling further investigations of their properties and potential application as sensor molecules.
Another type of aromatic diimides are perylene diimides. For example, Zang et al. have demonstrated a perylene diimide that can be used as an on-off single molecule fluorescent sensor. See Zang et al., J. Am. Chem. Soc. 2002, 124, 10640-1. A number of linear perylene diimides (FIG. 10) have been prepared from commercially available perylene anhydride or dianhydride and a wide array of amines via conventional imidization chemistry. Alkyl amines or amine terminated polyethylene glycols have been used to enhance solubility and/or impart liquid crystallinity. Approaches have also been reported to asymmetrically substituted diimides containing both a solubilizing group and a unit, e.g. an electron donor or acceptor, to endow a specific function to the perylene. See Langhals et al., Tetrahedron 2000, 56, 5435-41. Significant attention has also been given to attaching pendant groups directly to the perylene core, which can dramatically alter excited state properties. See Würthner. et al., J. Org. Chem. 2004, 69, 7933-9. However, the current synthetic methods for adding pendant substituents to perylene are limited both in terms of the types of substituents that can be attached as well as where they can be placed on the perylene. Greater flexibility in the types and placement of these substituents would enable the design of new perylenes with a wider range of spectral and sensory properties.
Accordingly, there remains a need in the art for fluorescent compounds that can be designed to sense a variety of different target molecules and fluoresce at a variety of different wavelengths. In addition, there remains a need for fluorescent compounds that exhibit high quantum yields and stability. Furthermore, there remains a need to develop procedures for readily synthesizing such fluorescent compounds.